Prediction of Relapse By microRNA Expression in Pediatric B-Lineage Acute Lymphoblastic Leukemia

Aim: microRNAs (miRs) have been implicated in many malignancies. Our aim was to identify specific miRNAs that can predict risk of relapse in pediatric acute lymphoblastic leukemia (ALL) patients treated on BFM protocols, better than the current risk group stratification. Currently, the main method for risk group stratification is based on the amount of minimal residual disease (MRD) assessed at specific time points by real time quantitative PCR (RQ-PCR).

Material and methods: Following microRNA expression analysis performed on 48 bone marrow samples at diagnosis, we focused on several miRs that correlated with at least 3 of the established prognostic markers in ALL to be validated in a cohort of 138 B-lineage ALL samples. Of the miRs studied, down regulated miR-151-5p and miR-451 and upregulated miR-1290 significantly correlated with outcome.

Results: Low expression of miR-151-5p, miR-451 or of both together resulted in significantly worse relapse free survival (RFS) (56%, 63% and 47%, respectively) compared to RFS rates when either or both miRs were highly expressed (80%, 78% and 78%, respectively) (p=0.007, 0.042 and 0.002, respectively). High expression of miR-1290 resulted in worse RFS compared to those that expressed low levels (54% versus 81%; p=0.014). When combining the 3 miRs, a patient expressing low levels of both miRs and/or high levels of miR-1290 had a RFS of 54% (p=0.004). Furthermore, the expression of the 3 miRs could distinguish within the TEL-AML1 negative cohort two groups; one with 80% and the other with 44% RFS (p=0.004). Multivariate Cox regression analysis identified low expression of both miRs and/or high expression of miR-1290 as an independent prognostic marker in the PCR-MRD non-high risk cohort. Patients expressing abnormal levels of the 3 miRs had a 4.47-fold increased risk for relapse (p=0.037). Deletion of IKZF1 gene is a known adverse prognostic marker in B-lineage ALL. In 85 patients, IKZF1 status was analyzed and 9 patients were found to harbor the deletion. The expression of the 3 miRs could still identify an adverse group of patients with 69% RFS within the group with no deletion (p=0.004). When adding IKZF1 and TEL-AML1 status to the Multivariate analysis in addition to PCR-MRD, the expression of the 3 miRs remained a significant independent marker with a 24 fold increased risk for relapse (p=0.011).

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Conclusion: Our results identify the combination of miR-151-5p, miR-451 and miR-1290 as a novel biomarker for outcome in pediatric B-lineage ALL patients, already at time of diagnosis. This may lead to improved risk group stratification and enable early therapeutic intervention that may result in better RFS.